Targeted desulfurization process and apparatus integrating gas phase oxidative desulfurization and hydrodesulfurization to produce diesel fuel having an ultra-low level of organosulfur compounds

ABSTRACT

Desulfurization of hydrocarbon feeds is achieved by flashing the feed at a target cut point temperature to obtain two fractions. A first fraction contains refractory organosulfur compounds, which boils at or above the target cut point temperature. A second fraction boiling below the target cut point temperature is substantially free of refractory sulfur-containing compounds. The second fraction is contacted with a hydrodesulfurization catalyst in a hydrodesulfurization reaction zone operating under mild conditions to reduce the quantity of organosulfur compounds to an ultra-low level. The first fraction is contacted with gaseous oxidizing agent over an oxidation catalyst having a formula Cu x Zn 1-x Al 2 O 4  in a gas phase catalytic oxidation reaction zone to convert the refractory organosulfur compounds to SO x  and low sulfur hydrocarbons. The by-product SO x  is subsequently removed, producing a stream containing a reduced level of organo sulfur compounds.

RELATED APPLICATIONS

None.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to integrated gas phase catalyticoxidative desulfurization processes to efficiently reduce the sulfurcontent of hydrocarbons.

2. Description of Related Art

The discharge into the atmosphere of sulfur compounds during processingand end-use of the petroleum products derived from sulfur-containingsour crude oil poses health and environmental problems. The stringentreduced-sulfur specifications applicable to transportation and otherfuel products have impacted the refining industry, and it is necessaryfor refiners to make capital investments to greatly reduce the sulfurcontent in gas oils to 10 parts per million by weight (ppmw) or less. Inthe industrialized nations such as the United States, Japan and thecountries of the European Union, refineries for transportation fuel havealready been required to produce environmentally clean transportationfuels. For instance, in 2007 the United States Environmental ProtectionAgency required the sulfur content of highway diesel fuel to be reduced97%, from 500 ppmw (low sulfur diesel) to 15 ppmw (ultra-low sulfurdiesel). The European Union has enacted even more stringent standards,requiring diesel and gasoline fuels sold in 2009 to contain less than 10ppmw of sulfur. Other countries are following in the footsteps of theUnited States and the European Union and are moving forward withregulations that will require refineries to produce transportation fuelswith an ultra-low sulfur level.

To keep pace with recent trends toward production of ultra-low sulfurfuels, refiners must choose among the processes or crude oils thatprovide flexibility that ensures future specifications are met withminimum additional capital investment, in many instances by utilizingexisting equipment. Technologies such as hydrocracking and two-stagehydrotreating offer solutions to refiners for the production of cleantransportation fuels. These technologies are available and can beapplied as new grassroots production facilities are constructed.

There are many hydrotreating units installed worldwide producingtransportation fuels containing 500-3000 ppmw sulfur. These units weredesigned for, and are being operated at, relatively milder conditions(i.e., low hydrogen partial pressures of 30 kilograms per squarecentimeter for straight run gas oils boiling in the range of 180°C.-370° C.). Retrofitting is typically required to upgrade theseexisting facilities to meet the more stringent environmental sulfurspecifications in transportation fuels mentioned above. However, becauseof the comparatively more severe operational requirements (i.e., highertemperature and pressure) to obtain clean fuel production, retrofittingcan be substantial. Retrofitting can include one or more of integrationof new reactors, incorporation of gas purification systems to increasethe hydrogen partial pressure, reengineering the internal configurationand components of reactors, utilization of more active catalystcompositions, installation of improved reactor components to enhanceliquid-solid contact, the increase of reactor volume, and the increaseof the feedstock quality.

Sulfur-containing compounds that are typically present in hydrocarbonfuels include aliphatic molecules such as sulfides, disulfides andmercaptans as well as aromatic molecules such as thiophene,benzothiophene and its long chain alkylated derivatives, anddibenzothiophene and its alkyl derivatives such as4,6-dimethyldibenzothiophene. Aromatic sulfur-containing molecules havea higher boiling point than aliphatic sulfur-containing molecules, andare consequently more abundant in higher boiling fractions.

In addition, certain fractions of gas oils possess different properties.The following table illustrates the properties of light and heavy gasoils derived from Arabian Light crude oil:

TABLE 1 Feedstock Name Light Heavy Blending Ratio — — API Gravity ° 37.530.5 Carbon W % 85.99 85.89 Hydrogen W % 13.07 12.62 Sulfur W % 0.951.65 Nitrogen ppmw 42 225 ASTM D86 Distillation IBP/5 V % ° C. 189/228147/244 10/30 V % ° C. 232/258 276/321 50/70 V % ° C. 276/296 349/37385/90 V % ° C. 319/330 392/398 95 V % ° C. 347 Sulfur SpeciationOrganosulfur Compounds ppmw 4591 3923 Boiling Less than 310° C.Dibenzothiophenes ppmw 1041 2256 C₁-Dibenzothiophenes ppmw 1441 2239C₂-Dibenzothiophenes ppmw 1325 2712 C₃-Dibenzothiophenes ppmw 1104 5370

As set forth above in Table 1, the light and heavy gas oil fractionshave ASTM (American Society for Testing and Materials) D86 85V % pointof 319° C. and 392° C., respectively. Further, the light gas oilfraction contains less sulfur and nitrogen than the heavy gas oilfraction (0.95 W % sulfur as compared to 1.65 W % sulfur and 42 ppmwnitrogen as compared to 225 ppmw nitrogen).

It is known that middle distillate cut boiling in the range of 170°C.-400° C. contains sulfur species including thiols, sulfides,disulfides, thiophenes, benzothiophenes, dibenzothiophenes, andbenzonaphthothiophenes, with and without alkyl substituents. (Hua, etal., “Determination of Sulfur-containing Compounds in Diesel Oils byComprehensive Two-Dimensional Gas Chromatography with a SulfurChemiluminescence Detector,” Journal of Chromatography A, 1019 (2003)pp. 101-109).

The sulfur specification and content of light and heavy gas oils areconventionally analyzed by two methods. In the first method, sulfurspecies are categorized based on structural groups. The structuralgroups include one group having sulfur-containing compounds boiling atless than 310° C., including dibenzothiophenes and its alkylatedisomers, and another group including 1, 2 and 3 methyl-substituteddibenzothiophenes, denoted as C₁, C₂ and C₃, respectively. Based on thismethod, the heavy gas oil fraction contains more alkylateddi-benzothiophene molecules than the light gas oils.

In the second method of analyzing sulfur content of light and heavy gasoils, and referring to FIG. 1, the cumulative sulfur concentrations areplotted against the boiling points of the sulfur-containing compounds toobserve concentration variations and trends. Note that the boilingpoints depicted are those of detected sulfur-containing compounds,rather than the boiling point of the total hydrocarbon mixture. Theboiling point of the key sulfur-containing compounds consisting ofdibenzothiophenes, 4-methyldibenzothiophenes and4,6-dimethyldibenzothiophenes are also shown in FIG. 1 for convenience.The cumulative sulfur specification curves show that the heavy gas oilfraction contains a higher content of heavier sulfur-containingcompounds and lower content of lighter sulfur-containing compounds ascompared to the light gas oil fraction. For example, it is found that5370 ppmw of C₃-dibenzothiophene, and bulkier molecules such asbenzonaphthothiophenes, are present in the heavy gas oil fraction,compared to 1104 ppmw in the light gas oil fraction. In contrast, thelight gas oil fraction contains a higher content of lightsulfur-containing compounds compared to heavy gas oil. Lightsulfur-containing compounds are structurally less bulky thandibenzothiophenes and boil at less than 310° C. Also, twice as much C₁and C₂ alkyl-substituted dibenzothiophenes exist in the heavy gas oilfraction as compared to the light gas oil fraction.

Aliphatic sulfur-containing compounds are more easily desulfurized(labile) using conventional hydrodesulfurization methods. However,certain highly branched aliphatic molecules can hinder the sulfur atomremoval and are moderately more difficult to desulfurize (refractory)using conventional hydrodesulfurization methods.

Among the sulfur-containing aromatic compounds, thiophenes andbenzothiophenes are relatively easy to hydrodesulfurize. The addition ofalkyl groups to the ring compounds increases the difficulty ofhydrodesulfurization. Dibenzothiophenes resulting from addition ofanother ring to the benzothiophene family are even more difficult todesulfurize, and the difficulty varies greatly according to their alkylsubstitution, with di-beta substitution being the most difficult todesulfurize, thus justifying their “refractory” appellation. These betasubstituents hinder exposure of the heteroatom to the active site on thecatalyst.

The economical removal of refractory sulfur-containing compounds istherefore exceedingly difficult to achieve, and accordingly removal ofsulfur-containing compounds in hydrocarbon fuels to an ultra-low sulfurlevel is very costly by current hydrotreating techniques. When previousregulations permitted sulfur levels up to 500 ppmw, there was littleneed or incentive to desulfurize beyond the capabilities of conventionalhydrodesulfurization, and hence the refractory sulfur-containingcompounds were not targeted. However, in order to meet the morestringent sulfur specifications, these refractory sulfur-containingcompounds must be substantially removed from hydrocarbon fuels streams.

Relative reactivities of sulfur-containing compounds based on theirfirst order reaction rates at 250° C. and 300° C. and 40.7 Kg/cm²hydrogen partial pressure over Ni—Mo/alumina catalyst, and activationenergies, are given in Table 2 (Steiner P. and Blekkan E. A., “CatalyticHydrodesulfurization of a Light Gas Oil over a NiMo Catalyst: Kineticsof Selected Sulfur Components,” Fuel Processing Technology, 79 (2002)pp. 1-12).

TABLE 2 4-methyl-dibenzo- 4,6-dimethyl- Name Dibenzothiophene thiophenedibenzo-thiophene Structure

Reactivity k_(@250), s⁻¹ 57.7  10.4  1.0 Reactivity k_(@300), s⁻¹ 7.32.5 1.0 Activation Energy 28.7  36.1  53.0  E_(a), Kcal/mol

As is apparent from Table 2, dibenzothiophene is 57 times more reactivethan the refractory 4,6-dimethyldibenzothiphene at 250° C. The relativereactivity decreases with increasing operating severity. With a 50° C.temperature increase, the relative reactivity of di-benzothiophenecompared to 4,6-dibenzothiophene decreases to 7.3 from 57.7.

The development of non-catalytic processes for desulfurization ofpetroleum distillate feedstocks has been widely studied, and certainconventional approaches are based on oxidation of sulfur-containingcompounds are described, e.g., in U.S. Pat. Nos. 5,910,440; 5,824,207;5,753,102; 3,341,448 and 2,749,284.

Oxidative desulfurization as applied to middle distillates is attractivefor several reasons. First, mild reaction conditions, e.g., temperaturefrom room temperature up to 200° C. and pressure from 1 up to 15atmospheres, are normally used, thereby resulting a priority inreasonable investment and operational costs, especially for hydrogenconsumption which is usually expensive. Another attractive aspect isrelated to the reactivity of high aromatic sulfur-containing species.This is evident since the high electron density at the sulfur atomcaused by the attached electron-rich aromatic rings, which is furtherincreased with the presence of additional alkyl groups on the aromaticrings, will favor its electrophilic attack as shown in Table 3 (Otsuki,et al., “Oxidative Desulfurization of Light Gas Oil and Vacuum Gas Oilby Oxidation and Solvent Extraction,” Energy & Fuels, 14 (2000) pp.1232-1239). However, the intrinsic reactivity of molecules such as4,6-DMDBT should be substantially higher than that of dibenzothiophene(DBT), which is much easier to desulfurize by hydrodesulfurization.

TABLE 3 Electron Density of selected sulfur species Electron K (L/Sulfur compound Formulas Density (mol.min)) Thiophenol

5.902 0.270  Methyl Phenyl Sulfide

5.915 0.295  Diphenyl Sulfide

5.860 0.156  4,6-DMDBT

5.760 0.0767  4-MDBT

5.759 0.0627  Dibenzothiophene

5.758 0.460  Benzothiophene

5.739 0.00574 2,5- Dimethylthiophene

5.716 — 2-methylthiophene

5.706 — Thiophene

5.696 —

Recently, the use of cobalt and manganese based catalysts in air basedoxidation of DBT type aromatic sulfur compounds into polar sulfonesand/or sulfoxides has been described. A wide number of transition metaloxides, including MnO₂, Cr₂O₃, V₂O₅, NiO, MoO₃ and Co₃O₄, or as welltransition metal containing compounds such as chromates, vanadates,manganates, rhenates, molybdates and niobates are described, but themore active and selective compounds were manganese and cobalt oxides. Itwas shown that the manganese or cobalt oxides containing catalystsprovided 80% oxidation conversion of DBT at 120° C. One advantage ofthese catalysts is that the treatment of fuel takes place in the liquidphase. The general reaction scheme for the ODS process suggested is asfollows: sulfur compound R—S—R′ is oxidized to sulfone R—SO₂—R′, and thelatter can decompose with heating, to liberate SO₂ and R—R′, whileleaving behind a useful hydrocarbon compounds that can be utilized. Arecommended temperature is from 90° C. to 250° C. See, PCT ApplicationNo. WO 2005/116169.

High catalytic activity of manganese and cobalt oxides supported onAl₂O₃ in oxidation of sulfur compounds at 130° C.-200° C. andatmospheric pressure has been described by Sampanthar, et al., “A NovelOxidative Desulfurization Process to Remove Refractory Sulfur Compoundsfrom Diesel Fuel,” Applied Catalysis B: Environmental, 63(1-2), 2006,pp. 85-93. The authors show that, after the subsequent extraction of theoxidation products with a polar solvent, the sulfur content in the fueldecreased to 40-60 ppmw. The thiophenes conversion increased with timeand it reached its maximum conversion of 80-90% in 8 hours. It was shownthat the tri-substituted dibenzothiophene compounds were easier to beoxidized than the mono-substituted dibenzothiophenes. The oxidativereactivity of S-compounds in diesel follows the order:tri-alkyl-substituted dibenzothiophene>di-alkyl-substituteddibenzothiophene>mono-alkyl-substituteddibenzothiophene>dibenzothiophene. These results showed that the mostrefractory sulfur compounds in the diesel hydrodesulfurization were morereactive in the oxidative desulfurization of fuel.

U.S. Pat. No. 5,969,191 describes a catalytic thermochemical process. Akey catalytic reaction step in the thermochemical process scheme is theselective catalytic oxidation of organosulfur compounds (e.g.,mercaptan) to a valuable chemical intermediate (e.g.,CH₃SH+2O₂→H₂CO+SO₂+H₂O) over certain supported (mono-layered) metaloxide catalysts. The preferred catalyst employed in this processconsists of a specially engineered V₂O₅/TiO₂ catalyst that minimizes theadverse effects of heat and mass transfer limitations that can result inthe over oxidation of the desired H₂CO to CO_(x) and H₂O.

The process described later by the inventors in PCT Application No. WO2003/051798 involves contacting of heterocyclic sulfur compounds in ahydrocarbon stream, e.g., in a petroleum feedstock or petroleum product,in the gas phase in the presence of oxygen with a supported metal oxidecatalyst, or with a bulk metal oxide catalyst to convert at least aportion of the heterocyclic sulfur compounds to sulfur dioxide and touseful oxygenated products as well as sulfur-deficient hydrocarbons andseparately recovering the oxygenated products separately from ahydrocarbon stream with substantially reduced sulfur. The catalyticmetal oxide layer supported by the metal oxide support is based on ametal selected from the group consisting of Ti, Zr, Mo, Re, V, Cr, W,Mn, Nb, Ta, and mixtures thereof. Generally, a support of titania,zirconia, ceria, niobia, tin oxide or a mixture of two or more of theseis preferred. Bulk metal oxide catalysts based on molybdenum, chromiumand vanadium can be also used. Sulfur content in fuel could be less thanabout 30-100 ppmw. The optimum space velocity likely will be maintainedbelow 4800 V/V/hr and temperature will be 50° C.-200° C.

The vapor-phase oxidative desulfurization of various sulfur compounds(such as: COS, or CS₂, CH₃SH, CH₃SCH₃, CH₃SSCH₃, thiophene and2,5-dimethylthiophene) by use of sulfur-tolerant V₂O₅-containingcatalysts on different supports has been taught by Choi, S., et al.,“Selective Oxidesulfurization of C1-Organosulfur Compounds overSupported Metal Oxide Catalysts,” Preprints of Symposia—AmericanChemical Society, Division of Fuel Chemistry, 47(1):138-139 (2002) andChoi S., et al., “Vapor-phase Oxidesulfurization (ODS) of OrganosulfurCompounds: Carbonyl Sulfide, Methyl Mercaptans and Thiophene,” Preprintsof Symposia—American Chemical Society, Division of Fuel Chemistry,49(2):514-515 (2004). In these papers, the feed gas contained 1000 ppmwof COS, or CS₂, CH₃SH, CH₃SCH₃, CH₃SSCH₃, thiophene and2,5-dimethylthiophene, 18% O₂ in He balance. The formed products(formalin, CO, H₂, maleic anhydride and SO₂) were monitored bytemperature programmed surface reaction mass spectrometry. It was shownthat the turnover frequency for COS and CS₂ oxidation varied by aboutone order of magnitude depending on the support, in the orderCeO₂>ZrO₂>TiO₂>Nb₂O₅>Al₂O₃—SiO₂.

A common catalyst for oxidative desulfurization is activated carbon (Yu,et al., “Oxidative Desulfurization of Diesel Fuels with HydrogenPeroxide in the Presence of Activated Carbon and Formic Acid,” Energy &Fuels, 19(2) pp. 447-452 (2005); Wu, et al., “Desulfurization of gaseousfuels using activated carbons as catalysts for the selective oxidationof hydrogen sulfide,” Energy and Fuels, 19(5) pp. 1774-1782 (2005)). Theapplication of this method allows removal of hydrogen sulfide fromgaseous fuels at 150° C. by oxidation with air (Wu, 2005) and alsosulfur removal from diesel fuels using hydrogen peroxide (Yu, 2005). Thehigher adsorption capacity of the carbon, the higher its activity in theoxidation of dibenzothiophene.

Various catalytic desulfurization processes are known, for instance,U.S. Pat. Nos. 7,749,376, 4,596,782, 3,945,914, and 2,640,010.

Nonetheless, demand remains for additional efficient and effectiveprocess and apparatus for desulfurization of hydrocarbon fuels to anultra-low sulfur level.

SUMMARY OF THE INVENTION

The above objects and further advantages are provided by the apparatusand process for desulfurization of hydrocarbon feeds containing bothrefractory and labile organosulfur compounds by mildhydrodesulfurization of a fuel stream to remove labile organosulfurcompounds and gas phase oxidative desulfurization of a targeted fractionto remove refractory organosulfur compounds.

None of the above-mentioned references describe a suitable andcost-effective process for desulfurization of hydrocarbon fuel fractionswith specific sub-processes and apparatus for targeting differentorganosulfur compounds. In particular, conventional methods do notfractionate a hydrocarbon fuel stream into fractions containingdifferent classes of sulfur-containing compounds with differentreactivities relative to the conditions of hydrodesulfurization andoxidative desulfurization. Conventionally, most approaches subject theentire gas oil stream to the oxidation reactions, requiring unitoperations that must be appropriately dimensioned to accommodate thefull process flow.

In addition, none of these references teach or suggest the use of acatalytic composition described herein for the effective removal ofsulfur containing compounds from gaseous phase hydrocarbons in anoxidative process.

Accordingly, new grassroots integrated systems or retrofitted systemsare provided herein capable of desulfurizing hydrocarbon fuel streamscontaining different classes of sulfur-containing compounds havingdifferent reactivities to produce hydrocarbon fuels with an ultra-lowsulfur level. The goal is achieved by integrating mildhydrodesulfurization and gas phase oxidative desulfurization ofrefractory organosulfur compounds, and utilizing reactions separatelydirected to labile and refractory classes of sulfur-containingcompounds. These systems provide this capability by utilizing reactionsseparately directed to labile and refractory classes ofsulfur-containing compounds. These new or retrofitted systems integratemild hydrodesulfurization and gas phase oxidative desulfurization ofrefractory organosulfur compounds.

As used herein in relation to the apparatus and process of the presentinvention, the term “labile organosulfur compounds” means organosulfurcompounds that can be easily desulfurized under relatively mildhydrodesulfurization pressure and temperature conditions, and the term“refractory organosulfur compounds” means organosulfur compounds thatare relatively more difficult to desulfurize under mildhydrodesulfurization conditions.

Additionally, as used herein in relation to the apparatus and process ofthe present invention, the terms “mild hydrodesulfurization” and “mildoperating conditions” when used in reference to hydrodesulfurization ofa mid-distillate stream, i.e., boiling in the range of about 180° C. toabout 370° C., generally means hydrodesulfurization processes operatingat: a temperature of about 300° C. to about 400° C., preferably about320° C. to about 380° C.; a reaction pressure of about 20 bars to about100 bars, preferably about 30 bars to about 60 bars; a hydrogen partialpressure of below about 55 bars, preferably about 25 bars to about 40bars; a feed rate of about 0.5 hr⁻¹ to about 10 hr⁻¹, preferably about1.0 hr⁻¹ to about 4 hr⁻¹; and a hydrogen feed rate of about 100 litersof hydrogen per liter of oil (L/L) to about 1000 L/L, preferably about200 L/L to about 300 L/L.

The cost of hydrotreating is minimized by operating under relativelymild temperature and pressure conditions. Deep desulfurization ofhydrocarbon fuels according to the present invention effectivelyoptimizes use of integrated apparatus and processes, combining mildhydrodesulfurization and gas phase catalytic oxidative desulfurization.Refiners can readily adapt existing hydrodesulfurization equipment andrun such equipment under mild operating conditions. Accordinglyhydrocarbon fuels are economically desulfurized to an ultra-low level.

Deep desulfurization of hydrocarbon feedstreams is achieved by firstflashing a hydrocarbon stream at a target cut point temperature toobtain two fractions. A first fraction contains refractory organo sulfurcompounds, including 4,6-dimethyldibenzothiophene and its derivatives,which boil at or above the target cut point temperature. A secondfraction boiling below the target cut point temperature is substantiallyfree of refractory sulfur-containing compounds. The second fraction iscontacted with a hydrodesulfurization catalyst in a hydrodesulfurizationreaction zone operating at mild conditions to reduce the quantity oforganosulfur compounds, primarily labile organosulfur compounds, to anultra-low level. The first fraction is contacted with a gaseousoxidizing agent over oxidation catalyst in a gas phase catalyticoxidation reaction zone to convert the refractory organosulfur compoundsinto hydrocarbons and SO_(x). The by-product SO_(x) is removed from theliquid by a separation system including gas liquid separators and/orstrippers and/or distillation columns and/or membranes. The processproduces a hydrocarbon product stream that contains an ultra-low levelof organosulfur compounds.

The inclusion of a flashing column in an integrated system and processcombining hydrodesulfurization and gas phase catalytic oxidativedesulfurization allows a partition of the different classes ofsulfur-containing compounds according to their respective reactivityfactors, thereby optimizing utilization of the different types ofdesulfurization processes and hence resulting in a more cost effectiveprocess. The cost of hydrotreating is minimized by operating underrelatively mild temperature and pressure conditions. The volumetric/massflow through the gas phase catalytic oxidation reaction zone is alsoreduced, since only the fraction of the original feedstream containingrefractory sulfur-containing compounds is subjected to the gas phasecatalytic oxidation process. As a result, the requisite equipmentcapacity, and accordingly both the capital equipment cost and theoperating costs, are minimized. In addition, the total hydrocarbonstream is not subjected to gas phase catalytic oxidation reactions, thusavoiding unnecessary oxidation of organosulfur compounds that areotherwise desulfurized using mild hydrodesulfurization.

Furthermore, product quality is improved by the integrated processdescribed herein since undesired side reactions associated withoxidation of the entire feedstream under generally harsh conditions areavoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention will be best understood when readin conjunction with the attached drawings. For the purpose ofillustrating the invention, there are shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the precise arrangements and apparatusshown.

FIG. 1 is a graph showing cumulative sulfur concentrations plottedagainst boiling points of three thiophenic compounds;

FIG. 2 is a schematic diagram of an integrated desulfurization systemand process; and

FIGS. 3A and 3B are postulated gas phase catalytic oxidativedesulfurization reaction mechanisms.

DETAILED DESCRIPTION OF THE INVENTION

An integrated desulfurization process is provided to produce hydrocarbonfuels with ultra-low levels of organosulfur compounds. The processincludes the following steps:

a. Flashing the hydrocarbon feedstock at a target cut point temperatureof about 300° C. to about 360° C., preferably about 340° C., to obtaintwo fractions. The two fractions contain different classes oforganosulfur compounds having different reactivities when subjected tohydrodesulfurization and oxidative desulfurization processes.

b. The organosulfur compounds in the fraction boiling below the targetcut point temperature are primarily labile organosulfur compounds,including aliphatic molecules such as sulfides, disulfides, mercaptans,and certain aromatics such as thiophenes and alkyl derivatives ofthiophenes. This fraction is contacted with a hydrodesulfurizationcatalyst in a hydrodesulfurization reaction zone under mild operatingconditions to remove the organosulfur compounds.

c. The organosulfur compounds in the fraction boiling at or above thetarget cut point temperature are primarily refractory organosulfurcompounds, including aromatic molecules such as certain benzothiophenes(e.g., long chain alkylated benzothiophenes), dibenzothiophene and alkylderivatives, e.g., 4,6-dimethyldibenzothiophene. This fraction iscontacted with a gaseous oxidant over oxidation catalyst in a gas phasecatalytic oxidation reaction zone to convert the organosulfur compoundsinto sulfur-free hydrocarbons and SO_(x).

d. The by-product SO_(x) is subsequently removed in a separation zonefrom the liquid products by apparatus that include gas-liquid separatorsand/or strippers and/or distillation columns and/or membranes.

e. The resulting stream from the hydrodesulfurization reaction zone andthe low sulfur stream from the separation zone can be recombined toproduce an ultra-low sulfur level hydrocarbon product, e.g., afull-range diesel fuel product.

Referring now to FIG. 2, an integrated desulfurization apparatus 6 isschematically illustrated. Apparatus 6 includes a flashing column 9, ahydrodesulfurization reaction zone 14, a gas phase catalytic oxidativedesulfurization reaction zone 16 and a separation zone 18. A hydrocarbonstream 8 is introduced into the flashing column 9 and fractionated at atarget cut point temperature of about 300° C. to about 360° C., and incertain embodiments about 340° C., into two streams 11 and 12.

Stream 11 boiling below the target cut point temperature is passed tothe hydrodesulfurization reaction zone 14 and into contact with ahydrodesulfurization catalyst and a hydrogen feed stream 13. Sincerefractory organosulfur compounds are generally present in relativelylow concentrations, if at all, in this fraction, hydrodesulfurizationreaction zone 14 can be operated under mild conditions.

The resulting hydrocarbon stream 15 contains an ultra-low level oforganosulfur compounds, i.e., less than 15 ppmw, since substantially allof the aliphatic organosulfur compounds, and thiophenes, benzothiophenesand their derivatives boiling below the target cut point temperature,are removed. Stream 15 can be recovered separately or in combinationwith the portion (20 a) boiling at or above the target cut pointtemperature that has been subjected to the gas phase catalytic oxidativedesulfurization reaction zone 16.

Stream 12 boiling at or above the target cut point temperature isintroduced into the gas phase catalytic oxidative desulfurizationreaction zone 16 to be contacted with a gaseous oxidizing agent and anoxidizing catalyst. The gaseous oxidizing agent can be an oxidant suchas oxides of nitrogen, oxygen, air, or combinations thereof. The higherboiling point fraction 12, the gaseous oxidizing agent and the oxidationcatalyst are maintained in contact for a period of time that issufficient to complete the C—S bonds breaking reactions. In the gasphase catalytic oxidative desulfurization zone 16, at least asubstantial portion of the aromatic sulfur-containing compounds andtheir derivatives boiling at or above the target cut point are convertedto SO_(x).

Stream 17 from the gas phase catalytic oxidative desulfurization zone 16is passed to the separation zone 18 to remove the SO_(x) as dischargegas stream 19 and obtain a hydrocarbon stream 20 that contains anultra-low level of sulfur, i.e., less than 15 ppmw.

Stream 20 a can be recovered alone or in combination with stream 15 toobtain a hydrocarbon product 21 that contains an ultra-low level ofsulfur. In alternative embodiments, the products can be separatelyrecovered.

Further, if the sulfur content of the oxidative desulfurization zoneproducts remains high and needs to be further reduced, it can berecycled as stream 20 b back to the hydrotreating zone 14.

In general, the oxidation catalyst can be selected from one or morehomogeneous or heterogeneous catalysts having metals from Group IB, IIB,IIIB and IIIA of the Periodic Table, including those selected from thegroup consisting of Cu, Ce, Zn and Al.

The gas phase catalytic compositions described herein are made bypreparing an aqueous solution of the nitrates of Cu, Zn, and Al, andoptionally Ce, and then combining this solution with an aqueous alkalinesolution which contains NaOH, and/or one or more of (NH₄)₂CO₃, Na₂CO₃and NH₄CO₃.

These solutions are combined at a temperature which may range from about50° C. to about 65° C., and at a pH in the range of from about 6.5 toabout 14. The resulting hydroxides, carbonates, and/or hydroxycarbonatesprecipitate are filtered, washed, and dried for at least ten hours at atemperature of at least 100° C. The resulting dried material is thencalcined for about 2-4 hours at a temperature of at least 450° C. toform compositions described in Examples 2-12. The precipitate may beaged prior to the filtering and washing, as elaborated in the examples.

The catalytic compositions comprise oxides of Cu, Zn, and Al in definedweight percent ranges, and optionally Ce. The weight percentages are inthe range of from 5 to 20 weight percent ZnO, from 10 to 50 weightpercent CuO, and from 20 to 70 weight percent of Al₂O₃. When Ce₂O₃ ispresent, its amount is in the range of from 0.1 to 10 weight percent ofthe composition. The compositions exhibit X-ray amorphous phase withhighly dispersed oxides of Zn, Cu, and optionally Ce.

The aforementioned structure has the chemical formulaCu_(x)Zn_(1-x)Al₂O₄, which is in accordance with the standard formulafor spinels, i.e., “MAl₂O₄,” where “M” signifies a metal or combinationof metals. Within the spinel, the ZnO and CuO are present as highlydispersed crystals. If Ce₂O₃ is present, it is in particle form, withparticles ranging in diameter from 5 nm to 10 nm. In certainembodiments, x is in the range of from 0.1 to 0.6, and in furtherembodiments from 0.2 to 0.5.

The compositions described herein preferably are granular in nature, andmay be formed into various shapes such as cylinder, sphere, trilobe, orquatrolobe. The granules of the compositions preferably have diametersranging from 1 mm to 4 mm.

The compositions have specific surface areas in the range of from 10m²/g to 100 m²/g, in certain embodiments from 50 m²/g to 100 m²/g, withpores ranging from 8 nm to 12 nm, in certain embodiments from 8 nm to 10nm. The weight percentages are in the range of from 20-45 for CuO, from10-20 for ZnO, and from 20-70 for Al₂O₃, in certain embodiments from30-45 for CuO, from 12-20 for ZnO, and from 20-40 for Al₂O₃.

The catalytic compositions are used in reactors such as fixed beds,ebullated beds, moving beds or fluidized beds.

It is frequently desirable to form composites of the catalyticcomposition, and this is preferably done by adding a binder to thecompositions prior to calcination. The binder may be, e.g., polyethyleneoxide, polyvinyl alcohol, aluminum pseudoboehmite, silica gel, ormixtures thereof. The binder may be added in amounts ranging from about1 wt % to about 20 wt % of the precipitate. The resulting mixture may beextruded through, e.g., a forming dye, and then dried, preferably atroom temperature for 24 hours, followed by drying at about 100° C. for2-4 hours. The extrusion product is then heated slowly, e.g., byincreasing temperatures by 2-5° C. every minute until a temperature of500° C. is reached, followed by calcinations at 500° C. for 2-4 hours.

In certain embodiments the feedstock, i.e., the sulfur containinghydrocarbon, will vary, but preferably is one with a boiling point above36° C., and in certain embodiments above 565° C. In further embodimentsthe hydrocarbon feedstream is a straight run gas oil boiling in therange of about 180° C. to about 450° C., typically containing up toabout 2 weight % sulfur, although one of ordinary skill in the art willappreciate that other hydrocarbon streams can benefit from the practiceof the system and method of the present invention.

The operating conditions for the gas phase catalytic oxidativedesulfurization zone 16 includes a weight hourly space velocity (WHSV)in the range of from 1 h⁻¹ to 20 h⁻¹, in certain embodiments 5 h⁻¹ to 15h⁻¹, and in further embodiments 8 h⁻¹ to 10 h⁻¹; a gas hourly spacevelocity (GHSV) in the range of from 1,000 h⁻¹ to 20,000 h⁻¹, in certainembodiments 5,000 h⁻¹ to 15,000 h⁻¹, and in further embodiments 5,000h⁻¹ to 10,000 h⁻¹; an operating pressure in the range of from about 1bar to about 30 bars, in certain embodiments about 1 bar to about 10bars, and in further embodiments about 1 bar to about 5 bars; anoperating temperature in the range of from about 200° C. to about 600°C., in certain embodiments about 250° C. to about 550° C., and infurther embodiments about 300° C. to about 500° C. The molar ratio ofO₂:C is generally about 1:100 to about 1:10, in certain embodimentsabout 1:50 to about 1:10, and in further embodiments about 1:20 to about1:10. The molar ratio of O₂:S is generally about 1:1 to about 150:1, incertain embodiments about 10:1 to about 100:1, and in furtherembodiments about 20:1 to about 50:1.

The hydrodesulfurization reaction zone is operated under mildconditions. As will be understood by one of ordinary skill in the art,“mild” operating conditions are relative and the range of operatingconditions depends on the feedstock being processed. According to thesystem described herein, these mild operating conditions as used inconjunction with hydrotreating a mid-distillate stream, i.e., boiling inthe range of from about 180° C. to about 370° C., include: a temperaturein the range of from about 300° C. to about 400° C., in certainembodiments from about 320° C. to about 380° C.; a reaction pressure inthe range of from about 20 bars to about 100 bars, in certainembodiments from about 30 bars to about 60 bars; a hydrogen partialpressure of below about 55 bars, in certain embodiments from about 25bars to about 40 bars; a feed rate in the range of from about 0.5 hr⁻¹to about 10 hr⁻¹, in certain embodiments from about 1.0 hr⁻¹ to about 4hr⁻¹; and a hydrogen feed rate in the range of from about 100 liters ofhydrogen per liter of oil (L/L) to about 1000 L/L, in certainembodiments from about 200 L/L to about 300 L/L.

The hydrodesulfurization catalyst can be, for instance, an alumina basecontaining cobalt and molybdenum, or nickel and molybdenum.

While not wishing to be bound by theory, the apparatus and process forreduction of sulfur levels of hydrocarbon streams described hereinincludes integration of mild hydrodesulfurization with a gas phasecatalytic oxidation reaction zone, in which the refractory organosulfurcompounds are desulfurized by breaking the C—S bonds as shown in FIG. 3Aand/or FIG. 3B. The sulfur in the hydrocarbon molecules are convertedinto SO_(x) and purged from the system in the gas phase throughflashing.

The present process and system offers distinct advantages when comparedto conventional processes for deep desulfurization of hydrocarbon fuel.The addition of a flash column into an the apparatus and process of theinvention that integrates a hydrodesulfurization zone and a gas phasecatalytic oxidative desulfurization zone uses low cost units in bothzones as well as more favorable conditions in the hydrodesulfurizationzone, i.e., milder pressure and temperature and reduced hydrogenconsumption. Only the fraction boiling at or above the target cut pointtemperature is oxidized in gas phase to convert the refractorysulfur-containing compounds to SO_(x). Traditional methods first oxidizethe organosulfur compounds to sulfoxides and sulfones and then removethem from the hydrocarbon mixture. The system described hereinselectively breaks the C—S bonds in the organosulfur compounds toproduce low-sulfur hydrocarbons and SO_(x). This results in morecost-effective desulfurization of hydrocarbon fuels, particularlyremoval of the refractory sulfur-containing compounds, therebyefficiently and economically achieving ultra-low sulfur content fuelproducts. Furthermore, the high operating costs and undesired sidereactions that can negatively impact certain desired fuelcharacteristics are avoided using the process and apparatus of describedherein.

EXAMPLES Example 1

A gas oil was fractionated in an atmospheric distillation column tosplit the gas oil into two fractions: a light gas oil fraction (LGO)that boils at 340° C. and less with 92.6 W % yield and a heavy gas oilfraction (HGO) that boils at 340° C. and higher with 7.4 W % yield wereobtained. The LGO boiling 340° C. or less, the properties of which aregiven in Table 4, was subjected to hydrodesulfurization in ahydrotreating vessel using an alumina catalyst promoted with cobalt andmolybdenum metals at 30 Kg/cm² hydrogen partial pressure at the reactoroutlet, weighted average bed temperature of 335° C., liquid hourly spacevelocity of 1.0 h⁻¹ and a hydrogen feed rate of 300 L/L. The sulfurcontent of the gas oil was reduced to 10 ppmw from 6,250 ppmw.

TABLE 4 Properties of Gas Oil, LGO and HGO Unit Gas Oil LGO HGO Yield W% 100 92.6 7.4 Sulfur W % 0.72 0.625 1.9 Density g/cc 0.82 0.814 0.885ASTM D86 Distillation  5% ° C. 138 150 332 10% ° C. 166 173 338 30% ° C.218 217 347 50% ° C. 253 244 355 70% ° C. 282 272 363 90% ° C. 317 313379 95% ° C. 360 324 389

The HGO fraction contained diaromatic sulfur-containing compounds(benzothiophenes) and triaromatic sulfur-containing compounds(dibenzothiophenes) with latter one being the most abundant species(˜80%) according to speciation using a two dimensional gaschromatography equipped with a flame photometric detector. Furtheranalysis by gas chromatography integrated with a mass spectroscopyshowed that benzothiophene compounds are substituted with alkyl chainsequivalent to four and more methyl groups.

The HGO fraction, the properties of which are given in Table 4, wassubjected to gas phase oxidative desulfurization using a gaseousoxidizing catalyst at 450° C., 1 atmosphere pressure, WHSV of 6 h⁻¹ andGHSV of 2084 h⁻¹ over a Cu—Zn—Al catalyst. The sulfur content of the oillayer was reduced to 11,400 ppmw from 19,000 ppmw. The hydrodesulfurizedLGO stream and gaseous oxidized HGO stream were combined to obtain adiesel product with 857 ppmw sulfur.

Examples 2-13

Examples 2-13 are provided which describe methods to make the gaseousoxidative desulfurization catalyst material (2-12) and tests using thosecatalysts (13).

Example 2

37.5 g of Cu(NO₃)₂ (0.2 moles), 13.3 g of Zn(NO₃)₂ (0.07 moles) and 50.1g of Al(NO₃)₃ (0.235 moles) were dissolved in 500 ml of distilled water,to form what shall be referred to as “solution A” hereafter. The pH ofthe solution was 2.3.

Similarly, 19.08 g of Na₂CO₃ (0.18 moles) and 36 g of NaOH (0.9 moles)were dissolved in 600 ml of distilled water, to produce “solution B,”which had a pH of 13.7.

Solution A was heated to 65° C. and solution B was added to solution Aat a rate of about 5 ml/minute with constant agitation, until all ofsolution B was added. The resulting mixture had a pH of 11.0. Aprecipitate formed which was aged for 6 hours at 65° C. The solution wascooled to room temperature and filtered with a Buchner funnel.Precipitate was washed with distilled water. Analysis of the precipitateshowed that nearly all (about 99%) of the Cu, Zn and Al precipitated outof the solution.

The precipitate was then dried at 110° C. for 12 hours. The driedmaterial was dark brown in color. Following drying, it was calcined at500° C. for 2 hours.

The calcined product contained 36 wt % elemental Cu, 12.1 wt % elementalZn, 14.2 wt % elemental Al and 0.02 wt % elemental Na. (In all of theexamples which follow, weight percent is given in terms of the pureelement, rather than the oxide.) In order to determine the weightpercent of the oxide in the composition, one divides the amount ofelement by its molecular weight, multiplies by the molecular weight ofthe oxide, and then normalizes to 100%. As an example, for thecomposition described herein, the wt % of Cu (36) is divided by themolecular weight of Cu, which is 63.54 to yield 0.567. This ismultiplied by the molecular weight of CuO, which is 79.54 to yield45.07. When similar operations are performed on the Zn and Al amounts,values of 15.56 and 53.66, respectively, are obtained, which normalizeto 39.43 wt % CuO, 13.61% ZnO, and 46.95 wt % Al₂O₃.

The atomic ratio of Cu:Zn:Al was 3:1:2.8. The product had a specificsurface area of 94 m²/g, a pore volume of 0.24 cm³/g, and an averagepore diameter of 9.5 nm. It exhibited highly dispersed CuO and ZnO, withan X-ray amorphous phase. “X-ray amorphous oxide phase” as used hereinmeans that, when observed via high resolution transmission electronmicroscopy (“HRTEM”), crystalline particles ranging from 2-10 nm, andusually 2-5 nm, were observed. Lattice parameters were very close tothose of spinels and its chemical composition found from EDXcorresponded to the formula Cu_(0.3)Zn_(0.7)Al₂O₄.

Example 3

A 500 ml sample of solution A was prepared according to the procedure inExample 2.

96.1 g of (NH₄)₂CO₃ (1 mole) was dissolved in 600 ml of distilled waterto produce “solution C,” which has a pH of 8.7.

Solution A was heated to 65° C., and solution C was added gradually tosolution A, with constant agitation. The combined solution had a pH of7.6.

Following combination of solutions A and C, a precipitate formed, whichwas aged for 1 hour at 65° C. The precipitate was filtered in the sameway the precipitate of Example 2 was filtered, and was then washed withroom temperature distilled water. Analysis showed that about 99% of Znand Al from the solution and 80-85% of Cu passed to the precipitate.

Precipitate was dried, as in Example 2, and then calcined at 500° C. for4 hours.

The resulting compound contained 26.3 wt % elemental Cu, 15.8 wt %elemental Zn, 22.3 wt % elemental Al, and the atomic ratio of Cu:Zn:Alwas 1.7:1:3.5. The compound had a specific surface area of 82 m²/g, apore volume of 0.29 cm³/g, and an average pore diameter of 12 nm. Itexhibited an X-ray amorphous oxide phase (Cu_(0.45)Zn_(0.55)Al₂O₄), andhighly dispersed CuO, which contained less than 50% of the total copper.

Example 4

A 500 ml sample of solution A was prepared according to the procedure inExample 2.

47.7 g (0.45 moles) of Na₂CO₃ and 18 g (0.45 moles) of NaOH weredissolved in 600 ml of distilled water, to produce solution B with a pHof 13.4.

Solution A was heated to 50° C., and solution B was added gradually, ata rate of 4 ml/min, with constant agitation. The resulting solution hada pH was 10.0.

A precipitate formed and was aged for 2 hours at 50° C. The precipitatewas filtered and washed with room temperature distilled water. Followingwashing, the precipitate was analyzed and found to contain about 99% ofthe Cu, Zn and Al of the amount initially contained in the solution, anda high amount of Na.

Following drying at room temperature for 12 hours, and then for 12 hoursat 110° C., the dark brown precipitate was calcined at 500° C. for 2hours.

The resulting product contained 40.5 wt % elemental Cu, 13.3 wt %elemental Zn, 13.8 wt % elemental Al, and 0.47 wt % elemental Na. Theatomic ratio of the components Cu:Zn:Al was 3.1:1:2.5. The compositionhad a specific surface area of 62 m²/g, a pore volume of 0.15 cm³/g, andan average pore diameter of 8.7 nm. As with the preceding examples, thecomposition exhibited an X-ray amorphous oxide phase(Cu_(0.2)Zn_(0.8)Al₂O₄), and a highly dispersed crystal phase whichcontained most of the Cu.

Example 5

The steps of Example 2 were followed, but the precipitate was filteredhot, and without aging. The calcined composition contained 40.2 wt %elemental Cu, 9.7 wt % elemental Zn, 17.2 wt % elemental Al, and 0.22 wt% elemental Na. The atomic ratio of Cu:Zn:Al was 4.2:1:4.3. The specificsurface area was 75 m²/g, and the pore volume was 0.29 cm³/g. Averagepore diameter was 12.5 nm. The phase composition was highly dispersed,crystalline phases of CuO, ZnO, and Al₂O₃.

Example 6

In this example, Example 3 was followed except 0.18 g of Ce(NO₃)₃(5.5×10⁻⁴ moles) was also added in the preparation of solution A. Afterthe precipitate was formed, it was aged for 6 hours at 55° C. Analysisof the calcined composition showed 20.9 wt % elemental Cu, 17.1 wt %elemental Zn, 23.9 wt % elemental Al and 0.5 wt % elemental Ce. Theatomic ratio of Cu:Zn:Ce:Al was 3.0:1:0.01:3.8. The composition had aspecific surface area of 83 m²/g, a pore volume of 0.20 cm³/g, and anaverage pore diameter of 10.0 nm. It exhibited an X-ray amorphous oxidephase with a composition of Cu_(0.5)Zn_(0.5)Al₂O₄ and a highly dispersedcrystalline phase of CuO, which contained less than 60% of the Cu, andalso a Ce phase, with particles not exceeding 5 nm in diameter.

Example 7

This example parallels Example 6, except the amount of Ce(NO₃)₃ wasincreased to 3.1 g (9.5×10⁻³ moles). Precipitation formation andfiltration were carried out at 65° C. for 6 hours.

The resulting calcined composition contained 20.2 wt % elemental Cu,15.1 wt % elemental Zn, 20.2 wt % elemental Al and 8.5 wt % elementalCe. Atomic ratios of Cu:Zn:Ce:Al were 1:35:1:0.25:3.2. The specificsurface area was 125 m²/g, with a pore volume of 0.3 cm³/g. Average porediameter was 8.0 nm. As with the other compositions, it exhibited anX-ray amorphous oxide phase and a formula of Cu_(0.5)Zn_(0.5)Al₂O₄. Italso exhibited a Ce phase with particles not greater than 10 nm indiameter.

Example 8

In this example, “solution A” contained 9.4 g of Cu(NO₃)₂ (0.05 moles),13.3 g of Zn(NO₃)₂ (0.07 moles) and 27.7 g of Al(NO₃)₂ (0.13 moles) in500 ml of distilled water. Solution A had a pH of 2.6. Solution Bcontained 53.0 g of Na₂CO₃ (0.5 moles) and 18 g of NaOH (0.45 moles) in600 ml of water. Solution B had a pH of 13.7.

The solutions were mixed and the resulting precipitate was separated, asin Example 2. The calcined composition contained 10 wt % elemental Cu,20.0 wt % elemental Zn, 21.3 wt % elemental Al and 0.65 wt % elementalNa. The atomic ratio of Cu:Zn:Al was 0.5:1:2.5, with a specific surfacearea of 112 m²/g, a pore volume of 0.30 cm³/g, and average pore diameterof 10.8 nm. The composition exhibited an X-ray amorphous oxide phaseformula Cu_(0.33)Zn_(0.67)Al₂O₄, and contained a highly dispersedcrystalline ZnO phase.

Example 9

In this example, solutions A and C were prepared in the same manner asthe solutions in Example 3.

Aging of the precipitate took place over 6 hours at 65° C. and pH 6.5,rather than 1 hour as in Example 3.

The resulting calcined product contained 10.0 wt % elemental Cu, 12.1 wt% elemental Zn, 33.8 wt % elemental Al and 0.05 wt % elemental Na. Theatomic ratio for Cu:Zn:Al was 0.84:1:6.7. The specific surface area was100 m²/g, the pore volume was 0.35 cm³/g, and the average pore diameterwas 11.0 nm. The composition exhibited the same X-ray amorphous oxidephase formula Cu_(0.4)Zn_(0.6)Al₂O₄, and there was a γ-Al₂O₃ phase aswell.

Example 10

In this example, Solution A contained 9.4 g of Cu(NO₃)₂ (0.05 moles),3.8 g of Zn(NO₃)₂ (0.02 moles), and 95.8 g of Al(NO₃)₂ (0.45 moles)dissolved in 500 ml distilled water. Solution A had a pH of 2.25.

Solution C contained 53.0 g of (NH₄)₂CO₃ (0.55 moles) dissolved in 600ml of distilled water. The pH of solution C was 8.0.

Precipitation, and separation of the precipitate, took place over 4hours at 65° C. and pH 6.5, to yield a composition containing 13.0 wt %elemental Cu, 4.2 wt % elemental Zn and 36.5 wt % elemental Al. Theatomic ratio for Cu:Zn:Al was 3.1:1:21. The specific surface area was150 m²/g, with a pore volume of 0.45 cm³/g, and an average pore diameterof 9.5 nm. The observed formula of the composition was ZnAl₂O₄ and Al₂O₃modified by Cu in the form of CuO.

Example 11

In this example, solution A contained 46.9 g of Cu(NO₃)₂ (0.25 moles),13.3 g of Zn(NO₃)₂ (0.07 moles), and 42.6 g of Al(NO₃)₂ (0.20 moles)dissolved in 500 ml of distilled water. Solution A had a pH of 2.3.Solution B contained 53.0 g of Na₂CO₃ (0.5 moles) and 12 g of NaOH (0.3moles) in 600 ml distilled water. Solution B had a pH of 13.3.

Precipitation conditions were same as those of Example 2, which did notpermit total precipitation of Al. In fact, while the precipitation of Cuand Zn was 99% that of Al did not exceed 80%. The resulting compositioncontained 50 wt % elemental Cu, 25.2 wt % elemental Zn, 7.4 wt %elemental Al and 0.85 wt % elemental Na. The atomic ratio of Cu:Zn:Alwas 2.0:1.0:0.7. The specific surface area was 50 m²/g, the pore volumewas 0.20 cm³/g, and the average pore diameter was 15.2 nm. The formulaof the composition was Cu_(0.33)Zn_(0.67)Al₂O₄, with highly dispersedcrystalline CuO and ZnO phases.

Example 12

In this example, solution A did not contain Al(NO₃)₂, but only 7.5 g ofCu(NO₃)₂ (0.04 moles), 3.8 g of Zn(NO₃)₂ (0.02 moles) and 45.7 g ofCe(NO₃)₃ (0.14 moles) dissolved in 500 ml of distilled water. Solution Ahad a pH of 4.2.

Solution D contained 15.0 g of (NH₄)₂CO₃ (0.16 moles) and 18.0 g ofNH₄HCO₃ (0.23 moles) in 600 ml distilled water. Solution D has a pH of8.0.

Following calcination, the composition contained 6.5 wt % elemental Cu,3.85 wt % elemental Zn and 78 wt % elemental Ce. The atomic ratio ofcomponents Cu:Zn:Ce was 1.7:1:9.5, and the specific surface area was 85m²/g, with pore volume of 0.23 cm³/g and average pore diameter of 10.9nm. The observed composition by XRD was a highly dispersed crystallineCeO₂ phase. Crystalline phases of Cu and Zn were not detected.

Example 13

The catalysts prepared in Examples 2-12 were tested for their ability tooxidatively desulfurize fuel oil containing sulfur-containing compounds.Fuels were prepared which contained thiophene, DBT (dibenzothiophene),and 4,6 DMDBT. The fuels were heated to gaseous state, and passed overthe catalytic compounds. In the Tables which follow, the formulation ofthe catalyst (“Cu—Zn—Al,” “Cu—Zn—Al—Ce,” or “Cu—Zn—Ce”) is followed by“(1)” or “(2)”. This refers to the nature of solutions B, C and D inExamples 2-12, with “(1)” referring to a Na containing solution (as insolution B) and “(2)” to an ammonium containing solution (as insolutions C and D). The final number indicates which example was used toproduce the catalyst.

The diesel fuel containing thiophene and DBT had the followingproperties: T₅₀ of 264, T₉₅ of 351, density of 0.841 Kg/1 at 20° C., and1.93 wt % of sulfur. Thiophene was oxidized with the catalyst preparedby the method in Example 2. Similarly, 4,6 DMDBT was oxidized with thecatalysts prepared by the methods in Examples 2, 3, and 6. Tables 5, 6,and 7 present these results.

TABLE 5 Oxidation of thiophene in octane solution HC T S Content GHSVWHSV S Removal Conversion Catalyst ° C. ppmw O₂/S h⁻¹ h⁻¹ W % W %Cu—Zn—Al (1)- 329 1000 59 22500 28 90 1.2 2

TABLE 6 Oxidation of DBT in toluene solution HC T S Content GHSV WHSV Sremoval Conversion Catalyst ° C. ppmw O₂/S h⁻¹ h⁻¹ W % W % Cu—Zn—Al(1)-2 300 800 80 2600 6 87 2.1 Cu—Zn—Al (2)-3 360 900 139 2900 6 53 3.5Cu—Zn—Al (1)-4 385 900 120 3700 8 69 3.9 Cu—Zn—A1(1)-5 370 900 95 3200 831 2.9 Cu—Zn—Al—Ce(2)-6 350 900 140 2900 6 55 3.1 Cu—Zn—Al—Ce(2)-7 400900 140 3100 6 26 3.0 Cu—Zn—Al (1)-8 350 1100 100 1700 6 33 1.3 Cu—Zn—Al(1)-9 340 1000 120 3900 6 48 3.7 Cu—Zn—Al (1)-10 400 1500 40 27000 28 661.7 Cu—Zn—Al (1)-11 340 1100 60 1500 6 24 3.3 Cu—Zn—Ce(2)-12 310 800 702600 6 22 1.9 Cu—Zn—Ce(2)-12 330 4100 30 4100 6 14 4.2

TABLE 7 Oxidation of 4,6-DMDBT in toluene solution T S Content GHSV WHSVS Removal HC Catalyst ° C. ppmw O₂/S h⁻¹ h⁻¹ % Conversion % Cu—Zn—Al(1)-2 312 900 140 2085 6 81 3.8 Cu—Zn—Al (2)-3 350 1000 140 2100 6 783.5 Cu—Zn—Al—Ce(2)-6 350 1000 140 2100 6 37 4.1

About 0.16 vol. % of H₂S, 0.118 vol. % of SO₂, and 5 vol. % of CO₂ werefound at the reactor outlet upon oxidation of the diesel fuel.

In these tables, “GHSV” refers to the gas volume rate (in liters/hourper liter of catalyst), “WHSV” means weight hourly space velocity: feedrate (Kg/hours) over the weight of the catalyst. “O₂/S” refers to therate at which oxygen was introduced to the material being tested. “S”and “HC” refer to “sulfur” and “hydrocarbon,” respectively.

The foregoing examples describe features of the invention which includea catalytic composition useful, e.g., in oxidative removal of sulfurfrom gaseous, sulfur containing hydrocarbons, as well as processes formaking the compositions, and their use.

The method and system of the present invention have been described aboveand in the attached drawings; however, modifications will be apparent tothose of ordinary skill in the art and the scope of protection for theinvention is to be defined by the claims that follow.

1. A method of processing a hydrocarbon feed to remove undesiredorganosulfur compounds comprising: a. flashing the hydrocarbon feedstockto provide a low boiling temperature fraction that contains a reducedlevel of organosulfur compounds and a high boiling temperature fractionhaving refractory organosulfur compounds; b. subjecting the low boilingtemperature fraction to a hydrodesulfurizing process to produce ahydrotreated effluent; c. contacting the high boiling temperaturefraction with a gaseous oxidizing agent and an oxidizing catalyst havinga formula Cu_(x)Zn_(1-x)Al₂O₄ wherein x ranges from 0 to 1 to convertrefractory organosulfur compounds into sulfur-free hydrocarbons andSO_(x) by breaking the C—S bonds; d. removing the by-product SO_(x) in aseparation zone from the sulfur-free hydrocarbons; and e. recovering anultra-low sulfur level hydrocarbon product.
 2. The method of claim 1,wherein the oxidizing catalyst comprises copper oxide in an amountranging from 10 weight percent (wt %) to 50 wt %, zinc oxide in anamount ranging from 5 wt % to less than 20 wt %, and aluminum oxide inan amount ranging from 20 wt % to 70 wt %, wherein said catalyticcomposition has an X-ray amorphous oxide phase, and highly dispersedcrystalline ZnO and CuO.
 3. The method of claim 1, wherein thetemperature cut point in step (a) is about 340° C.
 4. The method ofclaim 1, wherein the low boiling temperature fraction includes aliphaticorganosulfur compounds.
 5. The method of claim 4, wherein the aliphaticorganosulfur compounds include sulfides, disulfides, and mercaptans. 6.The method of claim 4, wherein the low boiling temperature fractionfurther includes thiophene and alkyl derivatives of thiophene.
 7. Themethod of claim 1, wherein the high boiling temperature fractionincludes dibenzothiophene, alkyl derivatives of dibenzothiophene andlong-chain alkylated derivatives of benzothiophene having a boilingpoint in the range of the high boiling temperature fraction.
 8. Themethod of claim 1, wherein the hydrocarbon feed is a straight run gasoil boiling in the range of about 180° C. to about 450° C.
 9. The methodof claim 8, wherein the hydrodesulfurizing process is operated at mildoperating conditions.
 10. The method of claim 9, wherein the hydrogenpartial pressure is less than about 55 bars.
 11. The method of claim 9,wherein the hydrogen partial pressure is about 25 bars to about 40 bars.12. The method of claim 9, wherein the operating temperature is about300° C. to about 400° C.
 13. The method of claim 9, wherein theoperating temperature is about 320° C. to about 380° C.
 14. The methodof claim 9, wherein the hydrogen feed rate in the hydrodesulfurizingprocess step is from about 100 liters of hydrogen per liter of oil toabout 1000 liters of hydrogen per liter of oil.
 15. The method of claim9, wherein the hydrogen feed rate in the hydrodesulfurizing process stepis from about 200 liters of hydrogen per liter of oil to about 300liters of hydrogen per liter of oil.
 16. The method of claim 1, whereinthe oxidizing agent is selected from the group consisting of oxides ofnitrogen, oxygen, and air.
 17. The method of claim 1, further comprisingrecovering a hydrotreated hydrocarbon product.
 18. The method of claim1, further comprising combining the low boiling temperature fractionthat has been subjected to a hydrodesulfurization process and the highboiling temperature fraction that has been subjected to gas phasecatalytic oxidative desulfurization by breaking the C—S bonds into areduced-organosulfur content hydrocarbon product.
 19. The method ofclaim 1 wherein the catalytic composition used in step (c) furthercomprises CeO₂ in the form of particles ranging in diameter from 5 nm to10 nm, in an amount ranging from 0.1 wt % to 10 wt % of said catalyticcomposition.
 20. The method of claim 1 wherein the catalytic compositionused in step (c) is in granular form.
 21. The method of claim 1 whereinthe catalytic composition used in step (c) is formed as a cylinder, asphere, a trilobe, or a quatrolobe.
 22. The method of claim 21 whereinparticles of the catalytic composition have effective diameter of from 1mm to 4 mm.
 23. The method of claim 21 wherein particles of thecatalytic composition have having a specific surface area of from 10m²/g to 100 m²/g.
 24. The method of claim 21 wherein particles of thecatalytic composition have having a specific surface area of from 50m²/g to 100 m²/g.
 25. The method of claim 21 wherein particles of thecatalytic composition have pores with effective diameters of from 8 nmto 12 nm.
 26. The method of claim 21 wherein particles of the catalyticcomposition have pores with effective diameters of from 8 nm to 10 nm.27. The method of claim 21 wherein particles of the catalyticcomposition have pores with a volume of from about 0.1 cm³/g to about0.5 cm³/g.
 28. The method of claim 1 wherein the catalytic compositionused in step (c) comprises from 20 wt % to 45 wt % CuO, from 10 wt % toless than 20 wt % ZnO, and from 20 wt % to 70 wt % of Al₂O₃.
 29. Themethod of claim 1 wherein the catalytic composition used in step (c)comprises from 30 wt % to 45 wt % CuO, from 12 wt % to less than 20 wt %ZnO, and from 20 wt % to 40 wt % Al₂O₃.
 30. The method of claim 1wherein x in the catalytic composition used in step (c) is from 0.1 to0.6.
 31. The method of claim 1 wherein x in the catalytic compositionused in step (c) is from 0.2 to 0.5.
 32. An apparatus for processing ahydrocarbon feed containing undesired organosulfur compounds comprising:a flashing column operable to flash a hydrocarbon feed at a temperaturecut point of about 320° C. to about 360° C., the flashing columnincluding an inlet for receiving the hydrocarbon feed, a low boilingtemperature outlet for discharging a low boiling temperature fraction,and a high boiling temperature outlet for discharging a high boilingtemperature fraction containing refractory organosulfur compounds; ahydrodesulfurization zone having an inlet in fluid communication withthe low boiling temperature outlet and an outlet for discharginghydtrotreated effluent; and a gas phase catalytic oxidativedesulfurization zone containing an oxidation catalyst and a gaseousoxidizing agent, gas phase catalytic oxidative desulfurization zonehaving an inlet in fluid communication with the high boiling temperatureoutlet, and an outlet for discharging low-sulfur hydrocarbons andSO_(x).